The present invention relates to image sensors and, more particularly, to forming photodiodes for image sensors.
Digital cameras are often provided with digital image sensors such as CMOS image sensors. Digital cameras may be stand-alone devices or may be included in electronic devices such as cellular telephones or computers. A typical CMOS image sensor has an image sensor pixel array containing thousands or millions of pixels. Each pixel typically includes a photosensor such as a photodiode that receives incident photons (light) and converts the photons into electrical signals.
In certain circumstances, image sensors may be used to capture near infrared light. Near infrared light may penetrate deep into a photodiode before being converted into electrical signals. Therefore, in order to ensure accurate sensing of near infrared light, a deep photodiode is required. Typically, photodiodes are formed by implanting n-type or p-type ions in a silicon substrate. However, a large amount of energy is required to implant ions deep enough for near infrared applications. These high energy implants may cause significant damage to the silicon substrate, resulting in high level of hot pixel and dark current. This may adversely affect the performance of the image sensor.
It would therefore be desirable to be able to provide improved methods for forming deep photodiodes in image sensors.